So I've been playing with combustions lately quite a bit. My old favorite 650 CI over/under was still my favorite until I recently recovered my bolt action 5' golf ball barrel, from the spudtech days, at a friends house where it had sat hidden for years, and created a new over/under. When I found it I cut the barrel off an old coaxial I had, 2'x3" chamber with a 1.5" barrel 20" into the chamber and a 3"x1.5" straight tee at the front for a handle, which also served as the fueling port and ignition.

I slapped a 1.5" P trap (a 180° coupler more or less) between the two, and created a monster. Seriously. I've chronied it at a buddies place, with a reputable chrony, and averaged 830 fps with MDX golfballs+mapp gas between 4 shots. The fifth hit the chrony . No more chrony, but luckily (for me) it was my buddy that shot it lol.

I have never had a standard combustion shoot so hard, at least for its size. A 200-some CI combustion shouldn't have the sharp kick of a rifle in my experience. I almost wonder if the combination of the ignition placement and coaxial open chamber (open as in the entire chamber portion of barrel is used as a chamber) is having something to do with it. Some sort of flame front speed increase or something. Thoughts?

No I haven't, my phone is my computer/internet source and it won't support HGDT. Perhaps if I got specs and a pic for reference someone here could run the numbers? I'm really curious about this, I've been spudding for 10 years and I've never seen this kind of power. It really does kick like a rifle, something like a .243 or around there. Kinda interesting watching my little brother shoot it, he's 13 and it kicks his ass every shot but he loves it.